The Great Basin Has No Drain

Rain that falls on Wheeler Peak runs downhill into creeks that flow east or west into the Snake Valley. From there it spreads across the valley floor and, eventually, disappears into the ground or evaporates. It does not reach the ocean. It does not reach any river that reaches the ocean. There is no such river. The entire Great Basin, a territory of roughly two hundred thousand square miles covering most of Nevada, western Utah, and portions of Oregon, Idaho, and California, has no external drainage. Every drop of water that enters it stays.

Geologists call this an endorheic basin, a closed basin. The mountains collect precipitation; the valleys evaporate it. The floors of the valleys are not river mouths but sinks, playas, and salt flats. The Great Salt Lake, Pyramid Lake, and Walker Lake are not connected to anything larger. They are the last remnants of water that entered their basins and had nowhere to go.

During the Pleistocene, roughly between twenty thousand and ten thousand years ago, the Great Basin was wetter and cooler. The Snake Valley you are driving through held springs and marshes. To the east, a vast inland sea called Lake Bonneville covered most of western Utah and portions of Nevada, reaching depths of nearly a thousand feet. To the northwest, Lake Lahontan covered several thousand square miles of western Nevada, leaving ancient shoreline terraces visible today on mountain flanks around Reno and Fallon.

When the climate warmed and dried at the end of the last ice age, those lakes evaporated down to their residuals: the Great Salt Lake, Pyramid Lake, Humboldt Sink. The desert you see in the valleys around Great Basin National Park is a bed of ancient lake sediment. The springs that still emerge from the valley floors are relict features of the wetter world, pressurized by groundwater accumulated over millennia in the aquifers beneath the basin.

Those aquifers were what Las Vegas wanted.